This invention relates generally to the continuous casting and rolling of metal rod, more particularly to an automated fluid cooling system for controlling the solidification of a cast bar product and to an automated fluid cooling and lubricating system for metal rod being rolled down from such a continuously cast bar.
In U.S. Pat. No. 3,279,000, entitled Apparatus For Continuous Casting of Metal, which is assigned to the assignee of this invention, there is disclosed a cooling system for a casting wheel wherein a cooling fluid is applied to a wheel-belt casting machine in three zones along the longitudinal pathway of the mold via a plurality of headers collectively supplied coolant under pressure via a main control valve which is paralleled with another coolant valve. A radiation pyrometer is used to control and regulate the flow of coolant to the various headers supplying coolant to the casting wheel via the coolant valve. By controlling the volume of coolant through the coolant valve it was possible to optimize the coolant supply to the casting wheel to provide a cast bar product with more consistent solidification properties than in prior art processes.
In the process disclosed in the aforementioned U.S. Pat. No. 3,279,000 the flow control valves were initially manually preset to achieve a predetermined rate of flow consistent with the desired solidification pattern for the cast bar product being produced, as required for entry into the subsequent step of hot-rolling the cast bar in a rolling mill. Since solidification may vary as a function of the cooling rate of the metal during casting of the bar, it is possible to vary such solidification by changing the settings of the flow control valves. This was accomplished at start-up by the casting machine operator based on his experience with the metal being cast (e.g., copper or aluminum, or alloys thereof). Thus, it was possible to process different metals and alloys, and to produce bar which accommodated the specific rolling mill requirements. The radiation pyrometer and its associated control apparatus was intended to correct for minor variations in cast bar temperature due to fluctuations in the cooling applied to the molten metal in the casting mold. However, the sensor was too slow and imprecise for effective control within the required response time, and the sensed temperature imprecision led to variations in the bar temperature which were often unacceptable.
In U.S. Pat. No. 3,766,763, entitled Continuous Rolled Rod Direct Cooling Method and Apparatus, which is assigned to the assignee of this invention, there is disclosed a cooling and lubricating system for a rolling mill wherein a water-soluble oil solution is provided to cool and lubricate the roll stands of a continuous rolling mill as well as to cool and descale the metal rod being rolled in the mill. The apparatus disclosed in U.S. Pat. No. 3,766,763 included a temperature sensing device located at the downstream end of the rolling mill for constantly monitoring the exit temperature of the rod and flow control valves responsive to the exit temperature for controlling the volume of coolant supplied to the roll stands and rod as it passed through the mill. By controlling the volume of coolant it was possible to optimize the rolling process and produce rod with more consistent metallurgical properties than in prior art processes.
In the process disclosed in the aforementioned U.S. Pat. No. 3,766,763 the flow control valves were manually preset to achieve a predetermined rate of flow consistent with the desired physical properties of the rod being produced, e.g., tensile strength, elongation, and, in the case of electrical conductor (E.C.) rod, conductivity. Since such properties may vary as a function of the cooling rate of the metal during rolling of the rod, it is possible to vary such properties by changing the settings of the flow control valves. This was accomplished manually by the mill operators based on their experience and empirical data. Thus, it was possible to process different metals and alloys, and to produce rod which accommodated the specific specifications of the customer.
In practice, the casting machine operator and the mill operator monitor the actual fluid flow rate and manually adjust the settings on the flow control valves to obtain a flow rate that each operator believes will yield cast bar or rod having the desired physical properties. The rod is then tested for tensile strength, elongation, conductivity, etc. and the flow control valves are manually re-adjusted if the rod properties are not as desired. This process of trial and error continues until the casting machine and mill are producing rod having the desired properties. It should be apparent, however, that it takes substantial time to set the casting machine and mill up correctly with manual valves since the casting machine and the mill must be running at a production rate in order for the flows to be adjusted correctly by the operators. Another problem has been that a large amount of scrap is generated during the set-up period at the start of a particular production run. Still another problem is that each operator on the multiple shift production line may perceive the correct flow rate differently from another operator, causing the rod produced for a particular customer to have inconsistent physical properties. Thus, the prior art manual process was inefficient and uneconomical.
These and other deficiencies in the prior art process have been overcome, in accordance with this invention, through the use of automatic control systems based on historical data of bar and rod previously produced. The automatic control systems are able to adjust the flow control valves during a production run if the bar and rod properties are outside the predetermined tolerance. This ensures that there will be no need to vary flow rates due to the use of different operators. The automatic flow control system is able to respond in the same manner every time, regardless of which operator is monitoring the casting machine and/or mill. This will optimize the corrective action and minimize the amount of out-of-tolerance rod being manufactured. Thus, it can be seen that the automatic coolant flow control systems of this invention are much more desirable than the manual valve and pressure gauge implementation used heretofore by multiple operators. These automatic control systems will reduce scrap rate, provide quality control, and eliminate casting machine and rolling mill down time due to malfunction, customer specification or operator error.
Automatic control systems employing a computer, programmable logic controllers, valves and flowmeters have been used to cast and water cool steel. However, such systems do not control or adjust flow rate on the basis of any historical data of the physical properties of the steel manufactured. Such systems also do not use any historical data to effect a change in variables monitored during the production process in order to obtain the desired physical properties of the metal. U.S. Pat. Nos. 4,483,387; 4,006,633; and 3,915,216 are exemplary of such systems. A computer operated system has also been used in the continuous casting of copper bar. In that system, the monitored variables of cast bar temperature and molten metal level in the casting machine are controlled by a computer.
U.S. Pat. No. 4,569,023 discloses a computerized system for controlling the temperature of metal being rolled into rod in a rolling mill. The system includes an arithmetic device for computing and controlling the rate of flow of cooling water based on the rolling schedule of the mill, the expected temperature of the rod at the inlet to the mill, and the target temperature of the rod at the exit of the mill.
In none of the above systems is control based on the desired physical properties of the final rod product and a measurement of actual physical properties of the final rod product.